public static void Test4()//引用类型：接口、委托、事件
{
//=========================接口
CDPlayer player1 = new CDPlayer();
player1.NextTrack();
player1.Open();
player1.CurrentTrack();
player1.NextTrack();
player1.NextTrack();
player1.CurrentTrack();
player1.PreviousTrack();
player1.CurrentTrack();
player1.Close();
Console.WriteLine();
//=========================显式接口
Computer cpt = new Computer();
ISystem sys = cpt;
sys.Run();
sys.Calculate();
ICalculator cal = cpt;
cal.Calculate();
Console.WriteLine();
//=========================委托
Say say1 = ASay;
Say say2 = BSay;
Say say3 = say1 + say2;
say1("Hi");
say2("Hi");
say3("Hello");
Console.WriteLine();
//=========================事件
Button button1 = new Button("Button1");
Button button2 = new Button("Button2");
button1.Click += Button1_Click; //订阅
button2.Click += Button1_Click; //订阅
//event1.myEvent += new MyEvent1.Handler(PrintParam);//订阅
button1.OnClick();
button2.OnClick();
//总过程：订阅，触发。事件调用委托，委托调用方法（方法参数是定义好的对象）。
button1.Click -= Button1_Click; //卸载订阅
button1.OnClick(); //已无效果
}